1. Field of the Invention
Recently, high power diode laser stacks have been widely used for surface treatment. A certain proportion of these applications require a defined track width and a uniform intensity distribution across the beam. When using a fixed beam spot size, the track has to be processed by successive laser runs. The surface is scanned with the laser beam and one processed area is put next to the other. Scanning of a surface has some drawbacks with respect to the process performance in creating that surface since consecutive application of the beam leads to irregularities of the surface structure. Therefore, a laser source with adjustable beam width is desirable.
To vary the spot size of the laser beam without time-consuming disassembly or un-attachment to the given optics, a variable optical set-up has to be used. This can be achieved with a varifocal lens or a zoom lens. However, these systems exhibit disadvantages, as such lenses are costly, heavy, and bulky and can create blurred spot sizes. The latter is mainly due to the high divergence angle of the diode laser beams.
Secondly, some diode laser stacks may not emit a laser beam that provides the required uniformity of its intensity distribution. It may exhibit peaks and dents that reduce the quality of the process. Therefore, an optic is desirable that flattens and homogenizes the intensity distribution of the laser beam over its width.
To overcome these disadvantages, a system is disclosed which provides a variable spot size using positionally adjustable reflective optics.
2. Description of Related Art
A system using light funnels for end-pumping of solid state lasers has been disclosed by Lawrence Livermore National Laboratory by Raymond J. Beach et. al., U.S. Pat. No. 5,307,430. The LLNL system disclosed is not adjustable and relies on total internal reflection to guide the beam. It is not designed for direct material processing with diode lasers.
The claimed invention is used to process a beam emitted from a light source, e.g. a diode laser, CO2 laser or Nd: YAG laser. The set-up consists of two reflective planes, which generally face each other, but exhibit an angle to each other that can be adjusted. The planes can converge or be parallel to each other. The space between the two planes can contain either air or any other optically transparent medium. The reflecting surfaces are designed as mirrors with a coating (e.g. dielectric or metal) or can be formed by total internal reflection.
By adjusting the mirrors, the beam width and the divergence angle are changed at the end of the set-up. The beam is imaged to the screen by a standard imaging optic. The imaging optic has a constant focal length. The variation of the spot size is performed through the variation of the angles of the reflectors, and thus no moving lenses are necessary.